Susceptibility of human influenza viruses to neuraminidase inhibitors (season 2008-2009)

Antiviral drugs play an essential role in managing infections caused by seasonal and pandemic influenza viruses. Due to the high prevalence of damantine resistance among seasonal influenza A viruses circulating in certain geographic regions, neuraminidase inhibitors (NAIs) are presently the only effective antiviral drugs for treatment and chemoprophylaxis of both seasonal and pandemic influenza infections. NAI susceptibilities of virus isolates collected during the 2008-2009 influenza season were assessed in the chemiluminescent neuraminidase inhibition (NI) assay. Among seasonal influenza A (H1N1) viruses tested, similar to 90% were outliers for oseltamivir and harbored the oseltamivir-resistance conferring H275Y mutation in the neuraminidase (NA), while only similar to 1% of pandemic 2009 influenza A (H1N1) viruses (H1N1pdm) were resistant to oseltamivir. All influenza A (H3N2) and B viruses were sensitive to oseltamivir, except for one A (H3N2) virus with D151V mutation, and an influenza B virus with D197E (D198E in N2 numbering) mutation in the NA. All viruses were sensitive to zanamivir, except for some seasonal influenza A (H1N1) and A (H3N2) outliers, which had no apparent changes in the NA besides the cell culture induced mutations at residue D151. All viruses tested for peramivir were sensitive to the drug, with the exception H275Y variants among seasonal A (H1N1) and H1N1pdm isolates, which exhibited reduced susceptibility. This study summarizes baseline NAI susceptibility profiles of seasonal and pandemic influenza viruses and contributes further criteria for defining resistance to NAIs.